The present invention concerns communication in a motor vehicle. In particular, the invention concerns a communication system including nodes in a bus and a motor vehicle having the communication bus.
In modern motor vehicles, information exchange between units and the control of various functions usually is performed with the help of communication buses. Naturally it is important that the signals transferred via the communication buses not be distorted during the transfer, as this could put the function and safety of the vehicle at risk. It is also important that a communication bus not radiate or leak electromagnetic energy in some other way in a manner such that other units in or outside of the vehicle are at risk of being disrupted or knocked out entirely. Various examples of solutions for mitigating this type of problem currently exist.
For example, U.S. Pat. No. 5,513,218 describes a serial communication bus in a motor vehicle, wherein a compensation circuit prevents the occurrence of mismatches that would otherwise potentially risk distorting signal pulses in the bus and cause undesirable radiation from it. The compensation bus includes an integrator, which simulates the ground voltage when the line ground voltage exceeds the voltage of the transmitting node. Said transmitting node is deactivated between the signal pulses in order to prevent the line voltage from increasing further. If, however, the voltage of the transmitting node falls below the line ground voltage, the transmitting node will remain active, including between the signal pulses, so as to increase the potential of the line ground voltage.
U.S. Pat. No. 6,031,823 describes a vehicle communication network that includes a circuit for ground translation and is intended to provide an interface with transmitter circuits in order to achieve smooth transitions. A communication bus is here adapted so as to be connected to a plurality of transceivers, wherein each transceiver is connected via a resistive element and supplies current to the bus when the transmitter voltage exceeds the bus voltage. The resistance thus added reduces the current changes that would otherwise occur in the bus when current sources are turned off and on.
The prior art also includes surrounding the signal cables in a communication bus with shielding that is in turn grounded for direct current in one of the network nodes while the shielding in all other nodes is grounded for alternating current only. This makes it possible to limit the undesired radiation of electromagnetic energy from the signal cables very effectively.